A PON system is one in which a station apparatus serving as an aggregate station is connected to terminals installed in a plurality of subscribers' homes by an optical fiber network that branches one optical fiber into a plurality of optical fibers through an optical coupler (see, for example, Japanese Patent Laying-Open No. 2004-64749 (FIG. 4) and Japanese Patent Laying-Open No. 2004-289780 (FIG. 31)). Upstream burst communication from the terminals to the station apparatus is managed in a time-sharing manner by the station apparatus in order to prevent signal collisions.
Although initially such upstream burst communication is considered at a certain transmission rate, in the future a stepwise increase in transmission rate is expected. However, even if provision of high transmission rate services begins, not all subscribers want the services at the same time, resulting in a multi-rate PON system in which for upstream communication, an existing transmission rate and a high transmission rate exceeding the existing transmission rate coexist in one PON system (see, for example, Japanese Patent Laying-Open No. 8-8954 (FIG. 2)).
In a multi-rate PON system such as that described above, for terminals registered (i.e., in operation) in the PON system, a station apparatus manages upstream communication in time-sharing manner. However, for example, a terminal that attempts to participate in the PON system by power-on from a power-off state is not yet recognized by the station apparatus at that point and thus the terminal does not have a chance to perform upstream communication. In view of this, periodically, a registration accepting process, called a discovery process, based on a standard, is performed.
However, even in such a case, since the terminal that attempts to participate is not yet under the control of the station apparatus, it is completely unknown at which transmission rate a registration request signal is to be transmitted. Accordingly, it is not always that the station apparatus always succeeds in receiving a registration request signal, and even if succeeded, it takes time to establish synchronization. Namely, the terminal that attempts to participate in the PON system cannot be promptly and reliably registered.